This paper presents a new methodology for the development of a probabilistic very long term forecast of the total port throughput in the Le Havre – Hamburg range up to 2100. The forecast is based on a combination of System Dynamic Modelling, Judgement, and Causal Relations. It is intended to provide infrastructure planners with some guidance on the very long term development of transport demand over the lifetime of the infrastructure. On the basis of the forecast it can be expected that the port throughput in the Le Havre – Hamburg region will remain growing throughout the first half of the century, but at a reduced pace. Towards the end of the century throughput volumes will stabilize or even decrease. The notion of decreasing and stabilizing throughput volumes will help infrastructure planners to consider the (ultimate) capacity to be provided beyond the current expansion plans as well as the type of expansions that will suit future demand some 20 to 30 years from now.